This invention relates to dot matrix copying devices suitable for ordinary office use. A typical copier of the type to which this invention applies is disclosed in Paranjpe et al, Ser. No. 789,417 filed Apr. 21, 1977, now U.S. Pat. No. 4,112,469. In the Paranjpe device there is a first lens which scans a document to be copied and a second lens which focuses a portion of the document upon an array of photodiodes. The first lens collimates the image of the document and directs a beam of collimated light upon a rotating mirror. The second lens receives collimated light reflected from the face of the rotating mirror for focusing upon the photodiodes. Output signals from the photodiodes provide switching control for an array of ink jets directed toward a copy paper mounted on a rotating drum. The drum is caused to rotate in synchronism with the rotation of the above mentioned mirror.
The Paranjpe apparatus has a problem in common with most office copiers. That is, the optics must view a large area in at least one dimension, and this is not readily achieved without use of very expensive lenses. The cost of such lenses may in some cases be excessive for such an application. The usual solution for this particular cost problem is one of compromise. That is, optics sre selected which will give marginal performance, with distortion at the edges of the field of view in an amount which is believed to be generally acceptable to the user. So far as is known, there is no available copy device which will provide accurate non-distorted reproduction over a wide scanning field of view with simple, modestly priced optics.